man ecpp (7): template-language for

DESCRIPTION

ecpp is the template-language used by the tntnet-system to generate dynamic content.

A template consists of normal content (normally html-data) enriched with special tags, which trigger some special handling.

One ecpp-file is compiled into a C++-class. The C++-class is placed into the namespace component. A ecpp-file compiled into a C++-class is called component. The name of the class is the basename of the file.

request, reply, qparam

Each component has 3 parameters: request, reply and qparam. request holds information about the client-request like http headers and the url, but also additional parameters specified in the config-file tntnet.xml(7). The type of request is tnt::HttpRequest.

reply receives the answer from the component. The component can set additional http-headers here, set cookies and - most important - generate output. The most important methods here are reply.out() and reply.sout(). Both return a std::ostream, which receives the output of the component. reply.sout() has a filter installed, which translates some characters, whith special meanings in html to the corresponding html-entities. The characters are <, >, &, " and '. This is useful for printing values from variables to the html-code.

qparam holds the query-parameters parsed from GET- or POST-parameters or received from other components. The type of qparam is tnt::query_params. Normally you use a <%args>-block to specify the parameters, but there are special cases, where it is useful to access these directly.

component adressing

Each component has a unique name. The name is composed from the class-name, the character '@' and the name of the shared library, it is located. Components can have internal subcomponents. The name of the internal subcomponent is appended to the classname separated by a dot (.).

special rule for line feeds after a </%something>-tag

A line feed immediately after a closing tag for all <%something>-blocks are ignored. Hence blocks followed immediately one after another does not generate white space in output, which is often undesirable.

error-handling

Error-handling is done by exception. Tntnet catches all exceptions thrown by components and handles them properly. Exceptions must be derived from std::exception. Exceptions derived from tnt::HttpError, are handled separately. They carry a http-return-code, which is sent to the client. Other exceptions derived from std::exception, result in a http error code 500 (Internal Server Error).

TAGS

<$ expr $>: Print expressions expr to the outputstream. The characters <, >, &, " and ', which have special meanings in html, are translated to the corresponding html-entities.
<$$ expr $>: Print expressions expr without translating characters with special meaning in html to html entities to the output stream.
<? cond ? expr ?>: Conditional output. Print expression expr to the outputstream, if cond evaluates to true. Characters with special meaning in html are translated to the corresponding html-entities.
<?? cond ? expr ?>: Conditional output. Print expression expr to the outputstream, if cond evaluates to true. Characters with special meaning in html are not translated to the corresponding html-entities.
<& component [ arguments ] >: Call the specified component. The output of the component is printed into the outputstream. If the component-name does not start with a letter, the ecpp-compiler treats it as a expression, which returns the name of the component. You must surround the expression in brackets, if it contains spaces.
: The arguments-part specify the parameters, the component will receive. Arguments are name-value-pairs separated by '='. They are put in the qparam-parameter of the component and are normally declared in the <%args>-block. Values can be specified in 3 forms:
: As a plain word without spaces
: As a string enclosed in quotation marks
: As a expression enclosed in brackets
: A single plain word in the argumentlist is treated as a variable of type cxxtools::query_params and a copy is passed to the component. Other parameters are added to this copy. If you want to pass all parameters of the current component put the variable qparam as a plain word in the argument list.
</&component>: Closing-tag for a component-call. When components are called, this closing-tag might occur later. The code in <%close>-block is placed here.
<{...}>: C++-inline-processing-block. The code in this block is copied into the C++-class unchanged.
: A linefeed after the closing tag is not ignored.
<#...#>: Comment-block. Everything in this block is ignored.
<%application [ scope="component|page|global" ] >...</%application>: Variables defined here, have the lifetime of the application.
: Application-scope is automatically locked.
<%args>...</%args>: Defines GET- or POST-parameters recieved by the component.
: Each argument has a name and optionally a defaul-value. The default-value is delimited by '=' from the name. A single argument-definition followed by a semicolon (;). In the component a variable with the same name of type std::string is defined, which receives the value.
: A argument-name can be prefixed by a type-definition. The ecpp-compiler generates code, which tries to convert the value with the input-stream-operator. This means, that each type, which can be read from a input-stream (std::istream) can be used. If the argument can't be converted, a exception is thrown.
: Argumentnames can be postfixed by empty square-brackets. This defines a std::vector with the specified type or std::string, if no type is specified. This way multiple values with the same name can be received. If a type is specified, each value is converted to the target-type.
<%close>...</%close>: Code in these tags is placed into the calling component, when a closing tag </&component> is found.
: The <%close> receives the same parameters like the corresponding normal component call.
<%config>...</%config>: Often webapplications need some configuration like database-names or login-information to the database. These configuratioin-variables can be read from the tntnet.xml. Variablenames ended with a semicolon are defined as static std::string-variables and filled from tntnet.xml. A variable can be prepended by a type. The value from tntnet.xml is then converted with a std::istream.
: You can also specify a default value by appending a '=' and the value to the variable.

Example:

<%config>
  dburl = "sqlite:db=mydbfile.sqlite";
  int maxvalue = 10;
</%config>

tntnet.xml:: <dburl>postgresql:dbname=mydb</dburl>
<%cpp>...</%cpp>: C++-processing-block. The code between these tags are copied into the C++-class unchanged.
: A linefeed after the closing tag is ignored.
<%def name>...</%def>: Defines a internal subcomponent with the name name, which can be called like other components.
<%doc>...</%doc>: Comment-block. Everything in this block is ignored.
: A linefeed after the closing tag is ignored.
<%get>...</%get>: Works like a <%args> block but receives only GET parameters.
<%i18n>...</%i18n>: Encloses a block of text-data, which is to be translated. See ecppl(1) and ecppll(1) for details.
<%include>filename</%include>: The specified file is read and compiled.
<%param>...</%param>: Defines parameter received from calling components. In contrast to query-parameters these variables can be of any type. The syntax (and the underlying technology) is the same like in scoped variables. See the description about scoped variables to see how to define parameters. The main difference is, that a parameter variable has no scope, since the parameter is always local to the component.
<%out> expr </%out>: Same as <$$ ... $>. Prints the contained C++ expression expr.
<%post>...</%post>: Works like a <%args> block but receives only POST parameters.
<%pre>...</%pre>: Defines C++-code, which is placed outside the C++-class and outside the namespace-definition. This is a good place to define #include-directives.
<%request [ scope="component|page|global" ] >...</%request>: Define request-scope variables. Variables defined here, has the lifetime of the request.
<%session [ scope="component|page|global" ] >...</%session>: Variables defined here, has the lifetime of the session.
: Sessions are identified with cookies. If a <%session>-block is defined somewhere in a component, a session-cookie is sent to the client.
: Sessions are automatically locked.
<%securesession [ scope="component|page|global" ] >...</%securesession>: Secure session is just like session but a secure cookie is used to identify the session. Secure cookies are transfered only over a ssl connection from the browser and hence the variables are only kept in a ssl secured application.
: If a variable defined here is used in a non ssl page, the variable values are lost after the current request.
<%sout> expr </%sout>: Same as <$ ... $>. Prints the contained C++ expression expr. The characters <, >, &, " and ', which have special meanings in html, are translated to the corresponding html-entities.
<%thread [ scope="component|page|global" ] >...</%thread>: Variables defined here, has the lifetime of the thread. Each thread has his own instance of these variables.
: Thread-scope-variables do not need to be locked at all, because they are only valid in the current thread.

SCOPED VARIABLES

Scoped variables are c++-variables, whose lifetime is handled by tntnet. These variables has a lifetime and a scope. The lifetime is defined by the tag, used to declare the variable and the scope is passed as a parameter to the tag.

There are 5 different lifetimes for scoped variables:

request: The variable is valid in the current request. The tag is <%request>.
application: The variable is valid in the application. The tag is <%application>. The application is specified by the shared-library of the top-level component.
session: The variable is valid for the current session. The tag is <%session>. If at least session-variable is declared in the current request, a session-cookie is sent to the client.
thread: The variable is valid in the current thread. The tag is <%thread>.
param: The variable receives parameters. The tag is <%param>.

And 3 scopes:

component: The variable is only valid in the same component. This is the default scope.
page: The variable is shared between the components in a single ecpp-file. You can specify multiple internal subcomponents in a %def-block. Variables, defined in page-scope are shared between these subcomponents.
global: Variables are shared between all components. If you define the same variable with global-scope in different components, they must have the same type. This is achieved most easily defining them in a separate file and include them with a <%include>-block.
: Variables are automatically locked as needed. If you use session-variables, tntnet ensures, that all requests of the same session are serialized. If you use application-variables, tntnet serializes all requests to the same application-scope. Request- and thread-scope variables do not need to be locked at all, because they are not shared between threads.

Syntax of scoped variables

Scoped variables are declared with exactly the same syntax as normal variables in c++-code. They can be of any type and are instantiated, when needed. Objects, which do not have default constructors, need to be specified with proper constructor-parameters in brackets or separated by '='. The parameters are only used, if the variable need to be instantiated. This means, that parameters to e.g. application-scope variables are only used once. When the same component is called later in the same or another request, the parameters are not used any more.

Examples

Specify a application-specific global variable, which is initialized with 0:

<%application>
unsigned count = 0;
</%application>

Specify a variable with a user-defined type, which holds the state of the session:

<%session>
MyClass sessionState;
</%session>

Specify a persistent databaseconnection, which is initialized, when first needed and hold for the lifetime of the current thread. This variable may be used in other components:

<%thread scope="global">
tntdb::Connection conn(dburl);
</%thread>

AUTHOR

This manual page was written by Tommi Mäkitalo